Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. However, the world demand for phenol is growing more rapidly than that for acetone. In addition, the cost of propylene is likely to increase, due to a developing shortage of propylene.
Thus, a process that uses higher alkenes instead of propylene as feed and coproduces higher ketones, such as cyclohexanone, rather than acetone may be an attractive alternative route to the production of phenols. For example, there is a growing market for cyclohexanone, which is used as an industrial solvent, as an activator in oxidation reactions and in the production of adipic acid, cyclohexanone resins, cyclohexanone oxime, caprolactam and nylon 6.
It is known from U.S. Pat. No. 5,053,571 that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a catalyst comprising ruthenium and nickel supported on zeolite beta and that the resultant cyclohexylbenzene can be processed in two steps to cyclohexanone and phenol. The hydroalkylation reaction is carried out at a liquid hourly space velocity (LHSV) ranging from 1 to 100, a reaction pressure ranging from 100 to 1000 kPa, a hydrogen feed rate ranging from 0.2 to 6 mole per mole of feedstock per hour, and a reaction temperature ranging from 100 to 300° C.
In addition, U.S. Pat. No. 5,146,024 discloses that benzene can be reacted with hydrogen in the presence of carbon monoxide and a palladium-containing zeolite X or Y to produce cyclohexylbenzene, which can then be converted in high yield to phenol and cyclohexanone by autooxidation with subsequent acid treatment. The hydroalkylation reaction is carried out at a liquid hourly space velocity (LHSV) of the benzene feed of about 1 to about 100 hr−1, a total reaction pressure of about 345 to about 10,350 kPa, a molar ratio of H2 to benzene of about 0.1:1 to about 10:1, a molar ratio of carbon monoxide to H2 of about 0.01:1 to about 0.3:1, and a temperature of about 100 to about 250° C.
Further, U.S. Pat. No. 6,037,513 discloses that cyclohexylbenzene can be produced by contacting benzene with hydrogen in the presence of a bifunctional catalyst comprising a molecular sieve of the MCM-22 family and at least one hydrogenation metal selected from palladium, ruthenium, nickel, cobalt and mixtures thereof. The catalyst may also contain a binder and/or matrix and in the Examples the catalyst is produced by impregnating an extrudate of the MCM-22 family molecular sieve and an alumina binder with an aqueous solution of a salt of the hydrogenation metal using incipient wetness impregnation. The '513 patent also discloses that the resultant cyclohexylbenzene can be oxidized to the corresponding hydroperoxide and the peroxide decomposed to the desired phenol and cyclohexanone.
According to the present invention, it has now been found that the benzene hydroalkylation activity of a bifunctional catalyst comprising a molecular sieve and a hydrogenation metal can be enhanced if some or all of the hydrogenation metal is supported on an inorganic oxide separate from, but composited with, the molecular sieve. Moreover the resultant catalyst exhibits enhanced selectivity to cyclohexylbenzene and dicyclohexylbenzene and reduced selectivity to cyclohexane, which is desirable since any dicyclohexylbenzene can be readily transalkylated with additional benzene to produce further cyclohexylbenzene product.